JP2007121430A - Flat image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display an image having improved uniformity of light emission and high image quality in an image display apparatus using an FED and an organic EL device. <P>SOLUTION: A threshold voltage measuring part VM measures the threshold voltage of a cathode line KL just before the end of one selection period for successively driving control electrode lines GL by using a display element FE having matrix structure for performing linear sequential drive in which luminance is specified by a current. The measured threshold voltage is recorded in each pixel and a drive signal for the selection of the pixel is corrected by using the value of the recorded threshold voltage to control charge discharged from a cathode K. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flat-panel image display apparatus that uses a light-emitting element whose luminance changes mainly by an electric current and controls the amount of electric charge that flows intermittently into a light-emitting portion, and in particular, adjusts the luminance of light emission. The present invention relates to a flat panel display capable of suppressing luminance variations due to a difference in electron emission start voltage, which is a threshold value at which emission of electrons from a cathode occurs.

  There is a current-driven display element whose light emission intensity is determined by the amount of charge incident on the light emitting layer from the electron emission source within a predetermined time, that is, current. Examples thereof include a field emission display (hereinafter referred to as “FED”) and an organic electroluminescence display (hereinafter referred to as “organic EL”).

  The FED obtains light emission by irradiating an electron beam from a large number of cold electron sources formed for each of a plurality of pixels toward a phosphor screen through a vacuum.

  In addition, there are several types of FED depending on the electron source used. The FED uses a Spindt type using a fine conical electron source, an electron source called a surface conduction type, and an ultrathin oxide film. There are those using an MIM type electron source and CNT-FED using a carbon nanotube (hereinafter referred to as “CNT”). The emission intensity of any electron source is as follows. It is determined by the voltage of the phosphor screen as the light emitting layer and the amount of electron beam irradiation to the phosphor screen within a unit time, that is, the current.

  Due to the characteristics of this phosphor, a high voltage of several kV or higher is used as the voltage on the phosphor screen. Therefore, it is common to apply a DC voltage, and the brightness of the FED depends on the incident electron dose that is exclusively the phosphor screen current. Change.

  Therefore, the incident electron dose is determined by changing the amount of electron emission from the electron source. For example, in Spindt type or CNT-FED, the amount of electron emission from the electron source is appropriate for the cathode and the control electrode. It is controlled by applying various voltages.

  Further, the MIM type and the surface conduction type do not have a configuration of a cathode and a control electrode, but in either case, a part of the current flowing by applying a voltage between the two electrodes is taken out into the vacuum as electron emission.

  On the other hand, in organic EL, light emission is obtained by injecting electrons from the cathode and holes from the anode into the light emitting layer formed for each pixel. The energy emitted by the recombination of electrons and holes injected into the light emitting layer, which is an organic thin film, causes an excited state in the light emitting layer, which is relaxed to emit light. Therefore, the emission intensity in the organic EL is generally determined by the number of electrons / holes injected into the light emitting layer within a unit time.

  That is, it is determined by the current flowing through the light emitting layer from the anode toward the cathode, but is generally controlled by the voltage applied to the anode and the cathode. (The electron emission from the cathode in the FED and the electron injection from the cathode in the organic EL are collectively referred to as “electron emission” hereinafter.)

  As described above, both the FED and the organic EL are driven by applying a predetermined electrode voltage regardless of the element whose emission intensity is determined by the current. In this case, there is a possibility that a luminance difference is generated for each pixel even when a predetermined electrode voltage is applied due to an influence of a difference in electrode voltage-electron emission characteristics in each of a plurality of pixels.

  In order to avoid this, direct control of the current flowing through the element has been studied, and a conventional technique for applying this to an organic EL is described in Patent Document 1 below.

  In this Patent Document 1, the light emission intensity of an organic EL is controlled by driving it with a constant current source connected to the cathode, and further, the floating capacitance at the time of transition from non-selection to selection in each cathode is controlled. Charging is performed from another large-capacity constant current source or constant voltage source. As a result, the time required for charging the stray capacitance is shortened, and the rising characteristics of light emission when the cathode is selected are improved to increase the responsiveness.

  A display element such as an FED or an organic EL has a matrix structure, and uses a line-sequential display method in which one of two kinds of electrodes constituting the matrix is sequentially selected.

  In this driving method, each pixel consists of a combination of two states, a short selection period and a relatively long non-selection period. Since one selection period is a short time, a change in luminance in the selection period is difficult for an observer to recognize. Therefore, even when light is emitted at a constant luminance during the selection period or when light is emitted strongly in a short time during the selection period, the same luminance is recognized as long as the luminance integration within one selection period is the same.

  A prior art in which a method for controlling the integrated light emission intensity within one selection period by controlling the total amount of charge flowing from the cathode power supply to the cathode within one selection period using this phenomenon is applied to the FED is disclosed in the following patent document. 2 and the prior art applied to organic EL are described in Patent Document 3 below. In these conventional techniques, a method is used in which the charge once charged in the stray capacitance or the external capacitance element is pulsedly emitted from the cathode.

  Since a display element such as an FED or an organic EL has a matrix structure, a region where the electrodes face each other is necessarily large, and each electrode has a stray capacitance. Furthermore, the capacity can be corrected by an external capacity. It is easier to reduce the variation in the total capacitance than to reduce the variation in the voltage-current characteristics of the electron-emitting devices, and the luminance variation between pixels can be reduced. Furthermore, since the charge charged to a known capacitor element is determined by the charge voltage applied to the element, a constant voltage source with a simple configuration can be used for driving.

  Here, FIG. 3 shows an interelectrode voltage-electron emission characteristic, so-called voltage-current characteristic, in an FED targeted by the present invention, and FIG. 11 shows an example of an interelectrode voltage-element current characteristic of an organic EL.

  In any element, as shown in FIG. 3, there is an electron emission starting voltage between the control electrode and the cathode in the FED, and as shown in FIG. 11, between the electrodes between the anode and the cathode in the organic EL. The voltage has a threshold value indicated as a light emission start voltage, and current does not flow below this threshold value. When the voltage exceeds this threshold, current suddenly starts to flow and light emission occurs. (Hereinafter, also in the organic EL element shown in FIG. 11, since light emission starts by electron emission from the cathode, it is referred to as “electron emission start voltage” including the light emission start voltage.)

  As described above, in order to cause electron emission from the cathode, the sum of the charge Qc necessary for the interelectrode voltage to reach the electron emission start voltage and the charge Qe necessary for obtaining light emission of a predetermined luminance is supplied. There is a need to. Since the charge Qc is also greatly affected by the stray capacitance of the cathode and the cathode line, the variation in the insulating film thickness that determines the stray capacitance in the FED element affects the required charge amount Qc.

  For this reason, Japanese Patent Application Laid-Open Publication No. 2004-228688 discloses a conventional technique that suppresses luminance variation between pixels by combining electron emission start voltage setting corresponding to variation in insulating film thickness and charge injection for emission.

  In this prior art, the interelectrode voltage is slightly lower than the electron emission start voltage even if the electron emission voltage is applied to the control electrode while the electron emission suppression voltage is applied to the control electrode in the first period at the time of pixel selection. The voltage V1 which becomes a voltage is applied to the cathode and charged.

Next, in addition to V1, a voltage for charging the charge Qe to be further discharged is applied, and then an electron emission voltage is applied to the control electrode. As a result, the electron emission with improved uniformity can be generated only by the voltage source.
Japanese Patent Laid-Open No. 11-231834 JP 2000-133116 A JP 2002-23688 A JP 2002-55652 A

  In the method of charging the electrode in the first period by the constant voltage source or the constant current source disclosed in Patent Document 1 and controlling the luminance by the constant current source in the second period, the configuration is more complicated than the constant voltage source. In addition to the problem that it is necessary to provide a constant current source that is expensive, it is difficult to set the charging conditions (voltage, current, time) in the first period, and it is not possible to cope with the time change of the element state of each pixel. .

  In addition, in the methods for controlling charges shown in Patent Documents 2 and 3, the drive circuit is not complicated because it can be realized with a circuit configuration almost the same as that of voltage drive by utilizing the stray capacitance. However, no consideration is given to the existence of an electron emission starting voltage which is a characteristic of the cathode. For this reason, there is a problem in that the amount of charge emitted from the cathode decreases by the amount of charge necessary for changing the electrode voltage to the start voltage without contributing to electron emission.

  In order to cope with this, the above-mentioned Patent Document 4 considers the electron emission start voltage, but the correction taking the electron emission start voltage into consideration only considers the insulating film thickness at the time of manufacture, that is, the stray capacitance between the electrodes. is not. In the FED cathode targeted by Patent Document 4, the surface state changes due to gas adsorption or the like in the atmosphere in contact with the surface. Such a change in the state of the cathode surface also occurs during the evacuation process after the electrode formation and during the display operation, and there is a possibility that the time change of the electron emission start voltage may occur accordingly.

  Further, in the technique disclosed in Patent Document 4, no consideration has been given to changes in the electron emission start voltage after the electrode structure is formed or during the subsequent operation. Furthermore, although only the FED is the subject of Patent Document 4, since the change of the interface state between each layer including the cathode during the operation also in the organic EL, the change in the electron emission start voltage for starting the light emission occurs. It is necessary to have a mechanism that can respond to changes in time.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a driving device that has a driving mechanism for controlling the amount of electric charge emitted from a cathode in an FED or an organic EL and that measures an electron emission starting voltage for starting light emission. By providing a mechanism that detects changes in the electron emission start voltage and corrects the drive signal based on the change, a flat-type image display device that has high emission uniformity and enables high-quality image display is provided. There is to do.

In order to achieve the above object, the present invention has the following structure. That is, (1) a pixel disposed at an intersection of a plurality of first electrode lines and a plurality of second electrode lines, a first electrode driver that applies a voltage according to a luminance signal to the first electrode lines, A flat panel image display device comprising: a second electrode driver that applies a selection voltage to the second electrode line; and a stray capacitance that temporarily holds a voltage corresponding to a luminance signal within a selection period based on the selection voltage. ,
A voltage measuring unit for measuring a voltage of the first electrode line immediately before the end of the selection period in a state where the first electrode driving unit opens the first electrode line; a recording table for recording a value of the measured voltage; This can be achieved by providing a voltage correction unit that corrects a voltage corresponding to the luminance signal applied to the first electrode line based on the value of the voltage.

  Further, the present invention performs a calculation process using the voltage value recorded in the recording table and the newly measured voltage value, and records the calculation result in the recording table as a new voltage value. An arithmetic processing unit is provided.

  In the present invention, the second electrode driving unit applies a non-selection voltage to the second electrode line, and the first electrode driving unit applies a voltage according to a luminance signal to the first electrode line to reduce the stray capacitance. After charging, the first electrode line is opened, and the second electrode driver applies a selection voltage to the selected second electrode line.

  According to the present invention, an external capacitor is added to the first electrode line.

  Furthermore, this invention has the following structures. That is, (2) a first electrode connected to the first electrode line and a second electrode connected to the second electrode line, wherein electrons emitted from the first electrode are lower than atmospheric pressure. The light is incident on the phosphor screen through the decompressed space, and the phosphor screen emits light to display an image.

  In the present invention, in the state where electron emission occurs from the first electrode, the first electrode voltage is Vk, the second electrode voltage is Vg, and the phosphor screen voltage is Vp, and the distance between the phosphor screen and the first electrode. Where dpk is dpk and the distance between the phosphor screen and the second electrode is dpg, dpk> dpg and Vg <(Vp−Vk) / dpk × (dpk−dpg) + Vk. It is characterized by that.

  In the present invention, the first electrode voltage is Vk, the second electrode voltage is Vg, and the phosphor screen voltage is Va in a state where electrons are emitted from the first electrode, and the distance between the phosphor screen and the first electrode. Is dpk, and the distance between the phosphor screen and the second electrode is dpg, the absolute value of dpk-dpg is less than the thickness of the thicker of the first electrode and the second electrode. Thus, a display element satisfying Vg ≦ Vk is used.

  In addition, the present invention is characterized in that a display element containing a fibrous carbon material is provided on the surface of the first electrode.

  Furthermore, this invention has the following structures. (3) A light emitting element having an organic light emitting layer between the first electrode and the second electrode is used.

  It should be noted that the present invention is not limited to the above-described configurations and the configurations described in the embodiments described below, and it goes without saying that various modifications can be made without departing from the technical idea of the present invention. .

  According to the present invention, in an image display device using a display element having a matrix structure in which luminance is determined by current rather than voltage represented by FED and organic EL, the difference in electron emission start voltage between pixels, that is, threshold voltage, operation The fluctuation of the threshold voltage in the medium can be corrected. As a result, it is possible to emit light with good luminance uniformity, and a flat image display device with high image quality can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Example 1 of a flat panel image display device using an FED according to the present invention will be described with reference to FIG. FIGS. 1A and 1B are diagrams showing the configuration of the control electrode and the cathode driving unit of this embodiment.

  As shown in FIG. 1, in this embodiment, an FED (FE) is used as a display element, a cathode (K) that emits electrons, a control electrode (G) that controls the electric field on the cathode surface, and a cathode (K ) Is mainly composed of three electrodes of a phosphor screen (P) that emits light by the incidence of electrons emitted from it.

  A matrix structure is formed by the plurality of cathode lines (KL) and the plurality of control electrode lines (GL), and a cathode (K) electrically connected to the cathode line (KL) at the intersection thereof, There is an electron beam source composed of a control electrode (G) electrically connected to the control electrode line (GL), and a pixel is formed together with a light emitting portion on the phosphor screen (P).

  A matrix structure is formed by the cathode line (KL) and the control electrode line (GL) connecting the respective electrode groups of the cathode (K) and the control electrode (G), and a surface facing the other electrode is also formed. Since it is large, each cathode line (KL) has a stray capacitance Ck.

  The cathode line (KL) is connected to a cathode drive unit (DK) capable of setting a voltage for each line, and can apply a set voltage Vb corresponding to a luminance signal to be emitted. By switching the drive unit, the open state, that is, the high impedance state can be obtained.

  On the other hand, a control electrode driver (DG) that can selectively apply an electron emission voltage (selection voltage) VgON and an electron emission suppression voltage (non-selection voltage) VgOFF to each control electrode line (GL). ) Is connected.

  Connected to the phosphor screen (P) is a high voltage phosphor screen power source (PP) that can give electrons sufficient energy for the phosphor (not shown) applied on the surface to emit light. Yes.

  A combination of sequentially selecting the control electrode line (GL) side and simultaneously applying voltage outputs corresponding to emission intensity required for pixels on the selected control electrode line to the cathode line (KL) side. Thus, desired electron emission is generated from the cathode surface constituting each pixel, and the emitted electron causes the phosphor on the phosphor screen (P) to emit light, thereby displaying a desired image.

  In this embodiment, a threshold voltage measuring unit (which can measure the cathode line (KL) voltage Vk by controlling the operation timing by a trigger signal (TR) synchronized with the operation of the control electrode driving unit (DG). VM).

  The threshold voltage measurement in the threshold voltage measuring unit (VM) is performed when the cathode line (KL) is disconnected from the cathode power source (PK) by the cathode driving unit (DK) and becomes a high impedance state. In FIG. 1 (a), the threshold voltage measurement unit (VM) is directly connected to the cathode line (KL). However, as shown in FIG. 1 (b), the interruption in the cathode drive unit (DK) is performed. Even if connected to the side, it can be measured. In addition, if a large amount of current flows through the threshold voltage measurement unit (VM), it leads to a measurement error and a decrease in the amount of emitted electrons. Therefore, it is desirable that the internal impedance of the threshold voltage measurement unit (VM) is high within a stable operating range. .

  In this embodiment, the stray capacitance Ck on the cathode line (KL) is utilized. However, when the stray capacitance alone is insufficient, or when the variation in stray capacitance between the cathode lines is extremely large, An external capacity can be added to each cathode line (GL). In this case, the external capacitance to be added is appropriately selected according to the state of the stray capacitance of each cathode line, so that it can be driven even by using a cathode driving unit (DK) having a narrow voltage variable range. it can. When an external capacitor is added, the result is the same as when the stray capacitance on the cathode line (KL) is large. Therefore, the description of the case where the external capacitor is added will be omitted below.

  Hereinafter, the driving procedure in the structure shown in FIG. 1 is shown in FIG. 2 showing the voltage change of each electrode and the current change due to electron emission, and the interelectrode voltage-electron emission intensity characteristics between the cathode and the control electrode used in the FED. This will be described with reference to FIG.

  FIG. 2 shows the voltage Vg (j) of the jth control electrode line that will be the selection control line, the voltage Vg (j + 1) of the next selection control electrode line, the cathode driver output voltage Vb for a certain cathode line, the drive The inflow current Ik from the part to the cathode line, the voltage Vk of the cathode line, and the current Ie due to the emitted electrons from the cathode are shown. Further, the interelectrode voltage Vgk between the control electrode and the cathode and the state of electron emission at each timing shown in FIG. 2 are represented by T0 to T3 in FIG.

  First, the voltage of all control electrode lines (GL) including the jth control electrode line (GL (j)) is set to the electron emission suppression voltage VgOFF by the control electrode power source (PG) and the control electrode driving unit (DG). (Time 0 (T0)). At this time, the interelectrode voltage Vgk is as indicated by T0 in FIG. 3, and no electron emission occurs.

  In this state, the cathode line (KL) connected to the cathode (K) from which electrons are to be emitted is connected to the cathode power source (PK) via the cathode driving unit (DK) to obtain a desired luminance. Is charged to the voltage Vb1 necessary for obtaining the voltage (first period (P1)).

  At this time, the value of the output voltage Vb1 is determined from the sum of the threshold voltage Vth of the cathode recorded in advance and the voltage determined from the amount of charge necessary for obtaining predetermined light emission. A method of determining the cathode drive unit output voltage Vb will be described later.

  Electrons flow into the cathode line (KL) to which the cathode driving output of the output voltage Vb1 is connected, so that the cathode line voltage Vk decreases toward Vb1.

  Although charges are stored in the stray capacitance Ck existing on the cathode line (KL), no electron emission occurs because the electron emission suppression voltage VgOFF is applied to all the control electrode lines (GL). The interelectrode voltage Vgk at this time moves to the position indicated by T1 in FIG. 3, but no electron emission occurs.

  Next, after a predetermined charge is stored in the stray capacitance Ck by the voltage Vb1, the connection between the cathode power source (PK) and all the cathode lines (KL) is cut off by the cathode driving unit (DK) (timing) 1 (T1)). In this state, neither the charging nor discharging is performed on the stray capacitance Ck, so that the cathode line voltage Vk is maintained (second period (P2)).

  Subsequently, the voltage Vg (j) of only the control electrode line (GL (j)) including the pixel that is to cause the electron emission by the control electrode driving unit (DG) is switched to the electron emission voltage VgON (timing 2 (T2 )).

  As a result, the control electrode voltage Vg (j) becomes VgON, the cathode voltage (Vk) becomes Vb1, and the interelectrode voltage Vgk becomes T2 shown in FIG. 3 to generate electrons. Therefore, electrons are emitted from the surface of the cathode (K) connected to the corresponding control electrode line (GL (j)), and the current Ie flows.

  With this electron emission, the charge charged in the stray capacitance Ck is discharged, the cathode line voltage Vk changes suddenly from Vb1, and the interelectrode voltage Vgk decreases (transition from T2 to T3 in FIG. 3). Since the electron emission intensity also decreases rapidly, pulsed electron emission occurs (third period (P3)). The maximum current Iep at this time is limited by the electric field applied to the cathode (K) surface.

  As the cathode line voltage Vk approaches the threshold voltage Vth, the interelectrode voltage Vgk approaches the electron emission start voltage and the electron emission current Ie decreases, so that the leakage current from the cathode line (KL) is sufficiently reduced. In this case, the cathode line voltage Vk does not exceed Vth.

  Therefore, immediately before the voltage Vg (j) of the selection control electrode line (GL (j)) is switched from the electron emission voltage VgON to the electron emission suppression voltage VgOFF (timing 3 (T3)), the cathode line (KL). Is the threshold voltage Vth of each cathode (K) present at the intersection with the jth control electrode line (GL (j)) that caused electron emission on each cathode line. Is measured by a threshold voltage measuring unit (VM) and recorded in a threshold voltage recording table.

  Thus, the operation of the pixel on the jth control electrode line (GL (j)) is completed, and the same operation is performed on the pixel on the next (j + 1) th control electrode line (GL (j + 1)). As described above, when the same operation is performed on all the control electrode lines and then the operation of the pixel on the jth control electrode line (GLj) is performed again, the value of the threshold voltage Vth recorded last time is used. By correcting Vb, the variation of the threshold voltage Vth can be corrected.

  Below, the setting method of the output voltage Vb of a cathode drive part (DK) is demonstrated.

  The emission brightness depends on the total amount of emitted electrons ΔQe within the third period. Then, the total amount of emitted electrons ΔQe is determined from the state of Vb1 at the timing (T2) when the voltage Vk of the cathode line that is one electrode of the stray capacitance Ck that the cathode line (KL) has with other electrodes or the like. This corresponds to the accumulated charge amount change ΔQ until the threshold voltage Vth is reached.

  During this time, since the other electrode voltages do not change, it is only necessary to consider the cathode line voltage Vk, and the amount of emitted electrons ΔQe is ΔQe = ΔQ = Ck (Vb1−Vth) (1).

  As shown in FIG. 3, the instantaneous electron emission intensity must also take into account the influence of the voltage between the electrodes and the electron emission intensity characteristic. However, as can be seen from the equation (1), the emission is performed within one selection period. The total amount of charge ΔQe is determined only by the stray capacitance Ck and the change width (Vb−Vth) of the cathode line voltage Vk. The stray capacitance can be measured when a light emitting element such as an FED is completed.

  Since the voltage Vb to be set is the cathode part output voltage Vb1, the threshold voltage Vth and the voltage width ΔVk = (Vb1−Vth) necessary for the charge amount change ΔQe = ΔQ are obtained.

  Obtaining the amount of charge ΔQb that needs to be emitted from the cathode within one selection period from the luminance to be emitted, the shape and light emission efficiency of the phosphor screen (P), the use efficiency of electrons derived from the number of scanning lines and the electrode shape, etc. Can do.

  From this ΔQb, the required voltage width ΔVk is ΔVk = (Vb1−Vth) = ΔQb / Ck (2).

  Therefore, if the threshold voltage Vth can be obtained, the output voltage Vb of the cathode driving unit can be obtained.

  The threshold voltage Vth can be measured by measuring the cathode line voltage Vk immediately before the timing 3 (T3) by the above method. The flow for using this for correcting the drive unit output voltage Vb will be described below with reference to FIG. Will be described with reference to FIG.

  FIG. 4 shows an example of the configuration of the control unit used in the image display apparatus. As the display element, an FED as shown in FIG. 1 is used, and the connection is as shown in FIG.

  In FIG. 5, a cathode drive unit (DK) that can apply different voltages to each of a plurality of cathode lines (KL), and an electron emission voltage is applied to zero or one of the plurality of control electrode lines (GL). And it connects via the control electrode drive part (DG) which can apply an electron emission suppression voltage to the other control electrode line (GL).

  Further, a threshold voltage measuring unit (VM) is connected to each of the cathode lines (KL), and a phosphor screen power source (PP) is connected to the phosphor screen (P). Note that a signal flow for displaying an image is general and thus omitted.

  A characteristic component of the present invention is a cathode driving unit having a blocking mechanism, and the structure thereof is the same as described with reference to FIG.

  In addition, a timing signal is connected so that the operations of the threshold voltage measurement unit and the threshold voltage storage table can be performed in synchronization with image display.

  As described with reference to FIG. 1, after the electron emission is generated in a state where the cathode line (KL) and the cathode driving unit (DK) in the display element are blocked, the control electrode voltage Vg is changed from the electron emission voltage VgON. Each pixel on the control electrode line (GL) to which the electron emission voltage VgON was applied is measured by measuring the cathode line voltage Vk immediately before switching to the electron emission suppression voltage VgOFF using the threshold voltage measurement unit (VM). The threshold voltage Vth of the cathode (K) that constitutes can be measured. The threshold voltage value thus measured is recorded for each pixel in the threshold voltage recording table.

  In this way, since the electron emission voltage VgON is sequentially applied to a plurality of control electrode lines (GL), by measuring the threshold voltage Vth of each cathode in synchronization with this, the cathode voltage of all the pixels is measured. The threshold voltage Vth can be measured and recorded.

  FIG. 5 shows only one measurement unit as the threshold voltage measurement unit (VM), but a threshold voltage measurement unit (VM) is connected to each cathode line (KL), and the control electrode line ( Every time one (GL) is selected and driven, the threshold voltages of all the cathodes constituting the pixels on the control electrode line (GL) can be measured.

  In the present embodiment, since the threshold voltage measuring units (VM) corresponding to the number of cathode lines are provided, all the control electrodes are sequentially selected and the threshold voltage Vth for all pixels is measured every time one screen is displayed. It is possible to correct the threshold voltage in near real time.

  However, by providing a separate cathode line switching mechanism, the threshold voltage Vth for all the pixels can be measured sequentially, but if the fluctuation of the threshold voltage Vth is gentle, the threshold of the number of systems smaller than that of the cathode line can be obtained. The effect of the present invention can also be obtained by providing a voltage measurement unit (VM).

  The threshold voltage value recorded in the threshold voltage recording table is read out when the corresponding pixel is selected from the next time onward, and the cathode driver output voltage Vb together with the image signal which is the input signal based on the equation (2). To decide. The determined voltage Vb is transmitted to the cathode driving unit via the D / A conversion and actually applied to the cathode line of the display element.

  By repeating such a cycle of threshold voltage measurement, recording, reading, cathode drive unit output voltage determination, and voltage application, it is possible to correct a luminance change when the threshold voltage Vth fluctuates.

  In FIG. 4, in order to measure the threshold voltage Vth, it is directly recorded in the threshold voltage recording table. However, as shown in FIG. 6, a calculation process using a newly measured value and a prerecorded value is performed. The result may be recorded as a new value in the threshold voltage recording table.

  As this calculation, for example, by performing a weighted averaging process, it is possible to suppress the influence of external noise, a single threshold voltage change, and the like, thereby preventing overcorrection. Needless to say, the contents of the arithmetic processing are not limited to averaging, and many methods are conceivable.

  Here, when the FED is used as the display element, light emitted is obtained when electrons emitted from the cathode (K) enter the phosphor screen (P), and the amount of electrons emitted from the cathode (K) is controlled. By doing so, the emission intensity is controlled.

  Even in the state where some of the emitted electrons are incident on the control electrode (G) due to the structure of the electrode, the electron emission start voltage exists in the inter-electrode voltage-electron emission intensity characteristic, and the amount of emitted electrons If the ratio of the incident amount to the control electrode is constant, the effect of the present invention can be obtained.

  However, in order to make full use of the effects of the present invention, there is no incidence of electrons on the control electrode (G), and the amount of charge emitted from the controlled cathode (K) is all incident charge on the phosphor screen (P). It is desirable to be an amount.

  7 and 8 show an electrode structure of the FED that can satisfy this condition and can effectively use the present invention. As shown in FIGS. 7 and 8, the FED is mainly composed of three types of electrodes: a cathode (K), a control electrode (G), and a phosphor screen (P).

  FIG. 7 shows a structure in which the control electrode (G) is disposed between the cathode (K) and the phosphor screen (P). In this structure, when the electron emission occurs, the voltage of the cathode (K) is Vk, the voltage of the control electrode (G) is Vg, the voltage of the phosphor screen (P) is Vp, and the phosphor screen (P) and the cathode ( K) is dpk, and the distance between the phosphor screen (P) and the control electrode (G) is dpg, dpk> dpg, and Vg <(Vp−Vk) / dpk × (dpk− dpg) By driving under the condition of + Vk, the electron beam emitted from the cathode (K) is focused near the control electrode (G), and the incidence to the control electrode (G) can be suppressed as much as possible. it can.

  Thereby, most of the electrons emitted from the cathode (K) can be incident on the phosphor screen (P), and the effect of the present invention can be effectively utilized.

  Further, as shown in FIG. 8, by placing the control electrode (G) at a position substantially the same height as the cathode (K), it is possible to suppress the incidence of electrons on the control electrode (G) and control the emission charge. The effect of can be utilized effectively. In such an electrode arrangement (hereinafter referred to as “IPG structure”), electrons emitted from the cathode are emitted toward the phosphor screen (P) to which a positive high voltage is applied. Do not pass in the vicinity of G). In particular, the average electric field Fpk between the phosphor screen (P) and the cathode (K) determined by the phosphor screen voltage Vp, the cathode voltage Vk, and the phosphor screen-cathode distance dpk = (Vp−Vk) / dpk (3) In particular, it is effective when a cathode material capable of obtaining sufficient electron emission even with a low electric field is used.

  Examples of such cathode materials include carbon nanotubes and carbon-based fiber materials having a nanometer size such as carbon nanofibers, and these are directly grown on the cathode base film or solvent. Then, a paste in which a resin agent or the like is mixed is printed, whereby a cathode capable of emitting electrons in a low electric field can be formed. For example, in a cathode formed by printing a paste of carbon nanotubes, sufficient electron emission can be obtained at about 3 V / μm.

  Using this cathode, the IPG structure shown in FIG. 8 is formed, and the phosphor screen-cathode (control electrode) distance dpk (= dpg) is 2 mm, the phosphor screen voltage Vp is 6 kV, and the control electrode interval is 150 μm. The control electrode voltage Vg and the cathode voltage Vk at the time of electron emission are both 0 V, and electron emission can be blocked by setting the control electrode Vg to −100 V or the cathode voltage Vk to +100 V.

  By combining this electrode voltage control, a matrix operation electron beam source can be configured, and as shown in FIG. 5, an FED can be configured by combining with a phosphor screen panel (P).

  The above shows the case where the FED is used as the display element. Next, Example 2 using an organic EL element as the display element will be described with reference to FIGS.

  FIG. 9 is a diagram showing a configuration of an electrode signal application unit of an image display apparatus using the organic EL element of this example, FIG. 10 is a diagram showing a film configuration of a light emitting unit of the organic EL element, and FIG. FIG. 12 is a graph showing an example of an interelectrode voltage-element current characteristic of an organic EL element to be used, FIG. 12 is a diagram showing a connection between a drive unit and an organic EL element as a display element, and FIG. 13 is an overall configuration diagram of an image display device.

  In FIG. 9, the display device of this example connects anodes and cathodes of a light emitting section (ELC) that is a pixel of an organic EL element (EL) of each pixel to connect anode lines (AL) and cathode lines ( KL), and applying a predetermined voltage to each line controls the light emission / non-light emission of the pixel.

  The light emitting part (ELC) has the film structure shown in FIG. 10, and on the anode (A), a hole injection layer (HIL), a light emitting layer (EM), an electron injection layer (EIL), a cathode These are stacked in the order of (K).

  When a voltage is applied to both ends of the light-emitting portion (ELC), the inter-electrode voltage-element current characteristic is shown as shown in FIG. 11. By applying a voltage higher than the electron emission start voltage, the element current flows and emits light. .

  Here, as shown in FIG. 9, the matrix structure is formed by the anode line (AL) and the cathode line (KL), and in the state where the device current does not flow by applying a voltage equal to or lower than the electron emission start voltage. , Affected by stray capacitance (Ck).

  Connected to each anode line (AL) is an anode driving section (DA) that can switch and apply two voltages, a selection voltage VaON and a non-selection voltage VaOFF, supplied by an anode power source (PA).

  On the other hand, the cathode line (KL) is supplied with the voltage supplied from the cathode power supply (PK) adjusted to a predetermined voltage Vb according to the luminance, or the cathode line (KL) is cut off from the cathode power supply (PK). Thus, a cathode driving unit (DK) that can be in a high impedance state is connected.

  Therefore, as shown in FIG. 12, the cathode driving unit (DK) and the anode driving unit (DA) are connected so that the voltages of the respective anode lines (AL) and cathode lines (KL) can be individually controlled. .

  When displaying an image, the anode line (AL) side is sequentially selected, and a voltage necessary for light emission of each pixel is applied to the cathode line (KL) side to display the image.

  In the following, an operation step when the light emitting unit (ELC) on the jth anode line (AL (j)) shown in FIG. 9 is caused to emit light will be described.

  First, the non-selection voltage VaOFF is applied to all the anode lines including the jth anode line. In this state, the cathode drive unit (DK) is switched to the cathode power source (PK) side, and the cathode line (KL) is connected to the jth anode line (AL (j)) and the intersection of each cathode line (KL). A voltage Vb necessary for light emission of the pixel is applied. Each cathode line (KL) has a stray capacitance Ck and is charged by the applied voltage. In this state, the anode voltage Va is the non-selection voltage VaOFF, and light emission does not occur because the voltage between the anode (A) and the cathode (K) is set to be equal to or lower than the electron emission start voltage (period 1). .

  Thereafter, the cathode drive unit (DK) is switched to the open side, the cathode line (KL) and the cathode power source (PK) are shut off, and then the selection voltage VaON is applied to the jth anode line (AL (j)). In the pixel on the cathode line charged in the period 1, an element current flows between the anode (A) and the cathode (K) in order to discharge the charged charge, and light emission corresponding to the charge amount is generated. On the other hand, in the pixel on the cathode line that has not been charged in the period 1, since there is no charge to be discharged, no element current flows and no light emission occurs (period 2).

  In the charged pixel, a peak current corresponding to the interelectrode voltage-element current characteristic shown in FIG. 11 flows, but the cathode line (KL) is cut off from the cathode power source (PK), so that the cathode (K ) Since the voltage gradually approaches the anode (A) and the inter-electrode voltage Vak reaches the electron emission start voltage, the device current stops flowing, so the inter-electrode voltage Vak does not fall below the electron emission start voltage.

  The integrated value of the device current amount before reaching the electron emission start voltage, that is, the amount of charge flowing through the device in one light emission period is the voltage Vb applied to the cathode line (KL) in period 1 as in the case of FED. It is represented by the difference from the threshold voltage Vth when the discharge ends and the stray capacitance Ck. This stray capacitance Ck can be measured.

  Further, in the discharge (light emission) period of period 2, since the applied voltage of the jth anode line (AL (j)) is sufficiently discharged immediately before switching from the selection voltage VaON to the non-selection voltage VaOFF, By measuring the voltage of each cathode line at the time, the threshold voltage Vth of the pixel on the jth anode line (AL (j)) can be measured by the threshold voltage measuring unit (VM).

  The voltage (Vb−Vth) necessary for charging the electric charge contributing to light emission can be obtained from the interelectrode voltage-element current characteristics, the light emission efficiency of the light emitting portion (ELC), and the stray capacitance Ck. Therefore, the voltage Vb to be applied in the period 1 can be obtained.

  With the configuration shown in FIG. 13, the line voltage scanning of the anode line and the threshold voltage measurement of each cathode line are combined, the threshold voltage of each pixel in the display element is measured by the threshold voltage measuring unit, and recorded in the threshold voltage recording table. . Correction is made based on the threshold voltage on the threshold voltage recording table, and a voltage value Vb necessary for obtaining the light emission intensity required by the luminance signal is obtained in the next light emission period.

  If this cycle of threshold voltage measurement, recording, and correction is performed in each display period (for example, every 1/60 seconds), brightness correction can be performed more accurately. An appropriate measurement cycle may be selected accordingly.

  By using the threshold voltage measurement and correction as described above, by controlling the amount of charge flowing through the pixel within one light emission period, the light emission is uniform even when the organic EL element is used as a display element as in the case of FED. A good image display device can be obtained. Needless to say, the correction unit having the calculation function shown in FIG. 6 is also effective when an organic EL is used as the display element.

The block diagram of the control electrode and cathode drive part in a FED image display apparatus. FIG. 5 is another configuration diagram of a control electrode and a cathode driving unit in the FED image display device. The graph showing the electrode voltage and electric current change in a FED image display apparatus. The graph showing the voltage between electrodes-electron emission intensity | strength characteristics in a FED image display apparatus. The block diagram of a FED image display apparatus. 1 is an overall configuration diagram of an FED image display device. The other block diagram of a FED image display apparatus. The figure showing an example of electrode arrangement | positioning of the FED element which has a control electrode between an anode and a cathode. The figure showing an example of electrode arrangement | positioning of the FED element with which a cathode and a control electrode are the same height. The block diagram of the cathode and anode drive part in the image display apparatus using an organic EL element. The figure showing the film | membrane structure of the light emission part of an organic EL element. The graph showing the interelectrode voltage-element current characteristic in an organic EL element. 1 is an overall configuration diagram of an image display device using an organic EL element. The block diagram of the image display apparatus using an organic EL element.

Explanation of symbols

FE ... field emission display element, P ... phosphor screen, G ... control electrode, K ... cathode, KL ... cathode line, GL ... control electrode line, Ck ... cathode line stray capacitance, PP ... phosphor screen power supply, PG ... control electrode Power supply, PK ... Cathode power supply, DG ... Control electrode drive unit, DK ... Cathode drive unit, VM ... Threshold voltage measurement unit, TR ... Cathode voltage measurement trigger signal, EL ... Organic EL element, ELC ... Organic EL light emission unit, A ... Anode, HIL ... hole injection layer, EM ... light emitting layer, EIL ... electron injection layer, AL ... anode line, PA ... anode power source, DA ... anode drive unit, e ... electron beam, dgk ... cathode-control electrode distance, dpg ... anode-control electrode distance, dpk ... anode-cathode distance, Vth ... threshold voltage, Vg ... control electrode line voltage, VgON ... electron emission voltage (selection voltage), VgOFF ... electron emission suppression voltage (non-selection voltage) , VaON ... Select Pole line voltage, VaOFF ... non-selection anode line voltage, Vk ... cathode line voltage, Vgk ... control electrode-cathode voltage, Vb ... cathode driver output voltage, Ik ... cathode line inflow current, Ie ... current due to electron emission, Iep ... peak value of current due to electron emission, P1 ... first period of driving (charge period to cathode line), P2 ... second period of driving (cathode line voltage maintaining period), P3 ... third period of driving (electron emission) Period), T0 ... start of one selection period (charge start), T1 ... first timing (charge end), T2 ... second timing (electron emission start), T3 ... third timing (threshold voltage measurement and one) End of selection period).

Claims (9)

A pixel disposed at an intersection of the first electrode line and the second electrode line, a first electrode driver for applying a voltage corresponding to a luminance signal to the first electrode line, and a selection voltage for the second electrode line In a flat-panel image display device having a second electrode driving unit that applies voltage and a stray capacitance that temporarily holds a voltage according to a luminance signal within a selection period based on the selection voltage,
A voltage measuring unit for measuring a voltage of the first electrode line immediately before the end of the selection period in a state where the first electrode driving unit opens the first electrode line; a recording table for recording a value of the measured voltage; And a voltage correction unit for correcting a voltage corresponding to a luminance signal applied to the first electrode line based on the value of the obtained voltage.   An arithmetic processing unit is provided that performs arithmetic processing using the voltage value recorded in the recording table and the newly measured voltage value and records the arithmetic result in the recording table as a new voltage value. The flat-panel image display device according to claim 1.   The second electrode driver applies a non-selection voltage to the second electrode line, and the first electrode driver applies a voltage according to a luminance signal to the first electrode line to charge the stray capacitance. 3. The flat panel image display device according to claim 1, wherein the electrode line is opened, and the second electrode driver applies a selection voltage to the selected second electrode line. 4.   4. The flat panel display according to claim 1, wherein an external capacitor is added to the first electrode line.   A first electrode connected to the first electrode line; and a second electrode connected to the second electrode line, wherein a space in which electrons emitted from the first electrode are depressurized lower than atmospheric pressure. 5. The flat panel image display device according to claim 1, wherein the image is displayed by being incident on the phosphor screen through the phosphor screen and emitting light. 6.   In a state in which electron emission occurs from the first electrode, the first electrode voltage is Vk, the second electrode voltage is Vg, and the phosphor screen voltage is Vp, and the distance between the phosphor screen and the first electrode is dpk, A display element in which dpk> dpg and Vg <(Vp−Vk) / dpk × (dpk−dpg) + Vk, where dpg is a distance between the second electrode and the second electrode is used. Item 6. The flat panel display according to Item 5.   In a state in which electron emission occurs from the first electrode, the first electrode voltage is Vk, the second electrode voltage is Vg, and the phosphor screen voltage is Va, the distance between the phosphor screen and the first electrode is dpk, When the distance between the second electrode and the second electrode is dpg, the absolute value of dpk−dpg is equal to or smaller than the larger one of the first electrode thickness and the second electrode thickness, and Vg ≦ Vk. 6. A flat panel image display apparatus according to claim 5, wherein a display element is used.   The flat panel display according to any one of claims 5 to 7, further comprising a display element including a fibrous carbon material on a surface of the first electrode. The flat panel display according to any one of claims 1 to 4, wherein a light emitting element having an organic light emitting layer between the first electrode and the second electrode is used.

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